The Effect of Continuous Positive Airway Pressure Treatment on Cardiovascular Reactivity in Patients with Obstructive Sleep Apnea

INTRODUCTION: Obstructive sleep apnea (OSA) is commonly associated with significantly elevated sympathetic activity throughout the day and during sleep (a time when sympathetic activity normally decreases). It is also well-known that chronically elevated sympathetic activity profoundly increases risk of cardiovascular disease and contributes to disease progression. Nevertheless, it is not clear whether OSA patients tend to have exaggerated stress responses similar to other patient populations. Despite documented improvements on blood pressure with use of continuous positive airway treatment (CPAP), it is unknown whether CPAP also improves the stress response in these patients. We tested the hypothesis that effective treatment of OSA (with CPAP) would reduce the autonomic-mediated stress response to voluntary apneas. We assessed cardiovascular reactivity as the pressor response to hypoxic apneas and also assessed baseline blood pressure and heart rate variability (indices of basal autonomic function) in treated and untreated OSA patients. METHODS: 22 OSA patients were recruited including 14 who were untreated and 8 who were effectively treated with CPAP for at least 3 months and had demonstrated treatment compliance and efficacy as determined by a high treatment success index. Subjects were fitted with a three lead electrocardiogram to measure the electrical activity of the heart, a pulse oximeter to observe continuous blood oxygen saturation and a Finometer to measure beat to beat arterial pressure through the duration of the study. Following a baseline period, subjects were then instructed to initiate a voluntary apnea (breathhold) lasting 20 sec. Data were collected electronically on to data acquisition system for subsequent analyses. RESULTS: The PAP-treated OSA subjects exhibited a lower BP response to apnea than treated subjects. CONCLUSION: These data demonstrate that CPAP decreases the pressor response to voluntary breathholds which is a form of stress. Previous studies in our lab have shown that these responses are primarily mediated by the sympathetic nervous system, thus these data suggest that the sympathetic response to stress is reduced in well-treated OSA patients. Finally, the decrease in sympathetic activity appears to be independent of any alterations of vagal outflow as no significant differences in the heart rate variability was observed.